O'Neill-class Colony
A Space Colony is an artificial habitat built by humans, usually at one of the Lagrangian points, to allow human habitation in space. The interior of each space colony usually replicates the surface of the Earth and the colony simulates gravity by rotating. An O'Neill cylinder consists of two very large, counter-rotating cylinders, each five miles (8 km) in diameter and twenty miles (32 km) long, that are connected at each end by a rod via a bearing system. They rotate so as to provide artificial gravity via centrifugal force on their inner surfaces.1 Artificial Gravity The cylinders rotate to provide artificial gravity on their inner surface. Due to their very large radii, the habitats would have to rotate only about forty times an hour to simulate a standard Earth gravity. Research on human factors in rotating reference frames indicate that almost no-one (at such low rotation speeds) would experience motion sickness due to Coriolis forces acting on the inner ear. People would be able to detect spin-ward and anti-spin-ward directions by turning their heads, and any dropped items would appear to be deflected by a few centimeters. The central axis of the habitat would be a zero gravity region, and it was envisaged that it would be possible to have recreational facilities located there. Atmosphere and Radiation The habitat was planned to have oxygen at partial pressures roughly like the Earth's air, 20% of the Earth's sea-level air pressure. Nitrogen would also be included to add a further 30% of the Earth's pressure. This half-pressure atmosphere would save gas and reduce the needed strength and thickness of the habitat walls. At this scale, the air within the cylinder and the shell of the cylinder provide adequate shielding against cosmic rays. Sunlight Large mirrors are hinged at the back of each stripe of window. The unhinged edge of the windows points toward the Sun. The purpose of the mirrors is to reflect sunlight into the cylinders through the windows. Night is simulated by opening the mirrors, letting the window view empty space; this also permits heat to radiate to space. During the day, the reflected Sun appears to move as the mirrors move, creating a natural progression of Sun angles. Although not visible to the naked eye, the Sun's image might be observed to rotate due to the cylinder's rotation. The light reflected from the mirrors is polarized, which might confuse bees. To permit light to enter the habitat, large windows run the length of the cylinder. These were not to be single panes, but would be made up of many small sections, to prevent catastrophic damage, and so the aluminum or steel window frames can take most of the stresses of the air pressure of the habitat. Occasionally a meteorite might break one of these panes. This would cause some loss of the atmosphere, but calculations showed that this would not be an emergency, due to the very large volume of the habitat. There is a Closed type of theres colonies where they don't have the windows or mirrors. Attitude control The habitat and its mirrors must be aimed at the sun. O'Neill and his students carefully worked out a method of continuously turning the colony 360 degrees per orbit without using rockets that discard reaction mass. First, the pair of habitats can be rolled by operating the cylinders as momentum wheels. If one habitat's rotation is slightly off, the two cylinders will rotate about each other. Once the plane formed by the two axes of rotation is perpendicular (in the roll axis) to the orbit, then the pair of cylinders can be yawed to aim at the sun by exerting a force between the two sun-ward bearings: away from each other will cause both cylinders to gyroscopically precess, and the system will yaw in one direction, towards each other will cause yaw in the other direction. The counter-rotating habitats have no net gyroscopic effect, and so this slight precession can continue for the habitat's orbit, keeping it aimed at the sun. Systems Alliance Colony History The Systems Alliance spend a good few years rebuilding their own Space colonies. During which 3 brand new ones were given to the Draconians to aid in saving them from extinction. To just simply give space colonies like these is no small matter and the Draconians realized this. This act weighed heavily in their decision to join the Systems Alliance. More were built in and around other systems where the Systems Alliance plans to, or has started, collecting raw materials. Links http://en.wikipedia.org/wiki/O%27Neill_cylinder